In the Nebulan assembly, Lord Zarak led a group who believed that the Autobot intentionally attacked Gort. Gort attempted to tell them that his fall was his own fault, but he was silenced. Galen, however, did not believe this. When the recorded message from Fortress Maximus was played for all to hear, Zarak interpreted the plea for a peaceful coexistence to be a lie, while Galen wanted to trust the aliens.
Blurr was sent to speak with the government of Nebulos. Zarak, determined to "prove" that the Autobots were hostile, had his bodyguard Krunk magnetize Blurr's arm while he was speaking. Immediately, the arm was attracted towards a metallic globe in the square, and the collision sent the ball crashing towards the people. The citizens panicked and ran for their lives, believing they were in the midst of an attack. Blurr, confused by the incident, left when he was fired at by the guards.
The overwhelming support of the people for the destruction of the Autobots forced Galen to mobilize the Nebulan army into the forest where the Autobot camp was. There, they attacked the surprised Autobots, who, under Fortress Maximus's orders, retreated further into the woods without firing back. In a desperate attempt to regain the Nebulans' trust, Fortress Maximus convinced several Autobots to surrender their heads to the Nebulans. Most of the others merely surrendered their weapons. Galen, touched by the gesture, promised to leave the remaining Autobots alone and kept the heads (and their bodies) and weapons in the main city, away from the Autobots.
Unhappy with the situation, Zarak had Vorath locate the radio frequency of the old Autobot base on Cybertron. Using this, they were able to contact Scorponok, who was leading a Decepticon contingent through the area to determine why it was deserted. Scorponok arrived on Nebulos, supposedly to help get rid of the Autobots, but instead captured Zarak and his group. They then proceeded to attack the main city, hoping to capture or destroy Fortress Maximus.
Faced with superior firepower, Galen turned to the scientist Arcana for help. He theorized the ability to bioengineer Nebulans to combine with the Autobot bodies by transforming into their heads, thus controlling them. Duros, Stylor, and Gort joined Galen and Arcana in allowing themselves to meld with the Autobots Fortress Maximus, Brainstorm, Highbrow, Hardhead, and Chromedome. The Nebulans then transformed into the Autobots' heads and fought back against the Decepticons. With their brainpower enhanced (a side-effect of the Headmaster process), the Autobots clearly fought better, and forced Scorponok to call a retreat.
Bitter at his defeat, Scorponok accepted a proposal from Lord Zarak to bioengineer him and his cronies into Headmasters as well. Unknown to Zarak, this would give him and Scorponok a joined mind. Zarak then created a tape showing him asking Galen to rescue him from Scorponok and had it sent. Galen, not aware of the Zarak-Scorponok alliance, led the Headmasters in an assault on the Decepticons. A Nebulan news crew, joined by Zarak's daughter Lyria, accompanied him.
On arriving, Galen was shocked to see Zarak, Vorath, Krunk, Spasma, Monzo, and Grax join up with the Decepticons Scorponok, Mindwipe, Snapdragon, Apeface, Skullcruncher, and Weirdwolf. In the midst of the ensuing battle, the news vehicle was shot down and the humans inside were hypnotized by Mindwipe. Under his control, they allowed themselves to be encased in strong-walled "bubbles" and washed over with anti-gravity beams. As they began to rise, Scorponok recognized Lyria and Zarak momentarily regained control of the melded mind. Foreshadowing his fate, however, Scorponok's will won out and Lyria was allowed to ascend to her doom along with the others.
The Autobots began rescuing the humans as soon as they realized what was happening, leaving themselves open to attack. The Decepticons took advantage of that and were able to knock all of them unconscious. Dazed by the hypnotic beam, both the news crew and Lyria could only recall that the Autobots appeared to be attacking them. Zarak regretted nearly getting his daughter killed, but believed that it was only a result of momentary battle lust.
The remaining Autobots went to help defend the Nursery, Nebulos's primary center for agricultural research, from Zarak's control. Upon discovering where the Autobots were, Zarak immediately led the Terrorcons to fight them off, because he wanted the Nursery for his own purposes. The battle revealed that in the absense of their weapons (surrendered to Galen earlier), the Autobots bioengineered the Nebulans code-named Recoil, Firebolt, Haywire, Pinpointer, Spoilsport, and Peacemaker to transform into the guns of Kup, Hot Rod, Blurr, Crosshairs, Sureshot, and Pointblank, giving them apparently enhanced firepower. Despite this, they were eventually forced to retreat when the Nursery was practically destroyed in the battle. Seeing this, Zarak finally realized that it was not he who was in control the the joined mind, but Scorponok.
Desperate to spare Nebulos from further war, Zarak helped Galen's men escape and told them about Earth, from where Goldbug had sent a distress signal. Galen realized, as had Zarak, that the only way to save Nebulos was to leave it. During the escape, they had to battle the new Decepticon Targetmasters: the Nebulans Fracas, Nightstick, Blowpipe, Caliburst, and Aimless binary-bonded with Scourge, Cyclonus, Triggerhappy, Slugslinger, and Misfire. As soon as they were reunited with the other Autobots, they left the planet for Earth. The Decepticons immediately followed left in pursuit. Soon after arriving on Earth, the two parties again clashed. In the battle, Galen was killed, and the human Spike Witwicky took his place.
In the years that followed, the Nebulan scientist Hi-Q, working with his partner Hi-Test, developed a bomb whose detonation would keep Transformers away by making all energy sources on the planet poisonous to Transformers. At the same time, he worked on an energy conversion process known as the Powermaster process.
The Decepticons Dreadwing and Darkwind arrived on the planet to discover what had happened to Scorponok's group. Taking Hi-Q's warnings to be a threat, they stayed on the planet and ingested its energy. As a result, the two became immobile and began dying of energy deprevation.
Hi-Test decided to strike out on his own and had his sidekick Throttle steal the secret of Powermaster conversion from Hi-Q. He then biomechanically engineered them both to transform into the Decepticons' engines. Thusly, they were able to power them by converting organic nutrients into energy usable by the Decepticons. In return, Hi-Test had enough power to dominate the planet.
The Autobots Goldbug, Joyride, Getaway, and Slapdash arrived onto the planet with the personality of former Autobot leader Optimus Prime on a computer disk. There, they asked Hi-Q to help them build a new body for Prime. Hi-Q agreed, but warned them about the poisoned fuel. Following an incident defending several Nebulans from Dreadwing and Darkwing, the Autobots (except for Goldbug, due to his exceptional efficiency) became dangerously low on fuel. However, they continued working on Optimus's body until it was completed. To save the Autobots, Hi-Q, Rev, Lube, and Hotwire agreed to undergo the Powermaster process and bond with the Autobots. Optimus's new abilities allowed him to easily beat the two Decepticons, and they were exiled from the planet. The Autobots then left the planet with their new Nebulan partners.
There have been no other known instances where Transformers visited Nebulos. Kreb, Brisko, and Loco (bonded to Horri-bull, Fangry, and Squeezeplay) may have left Nebulos at the same time Zarak did, and only appeared after arriving on Earth. It is also possible they are not actually Nebulans, but merely Terrans (regardless of what the tech specs say).